The use of partially permeable materials, e.g., one of the so-called gas barrier plastics, presents a novel problem in the packaging of perishable commodities, such as edible oils and fats, other foods, carbonated beverages, wine and beer, and also of other materials that are affected by continuing exposure to the atmosphere. The problem derives from the fact that, in contrast to the materials customarily used for packaging under such conditions, namely glass and metal, these materials are partially permeable and thus do not provide absolute protection because they are never completely impervious.
The art has developed materials that are relatively impervious to given substances. These "better" materials tend to be more expensive, and despite the added cost even they have a finite permeability.
For example, in the field of plastics the approach taken heretofore was to develop barrier polymers with better permeation impedance for specific substances, such as oxygen carbon dioxide, water vapor, aromatics, etc. These efforts did meet with considerable success. Thus, for example, the permeation rate of oxygen was reduced by a factor of several orders of magnitude from polystyrene to the newly developed acrylonitrile copolymers, or to a lesser degree to terephtalic polyesters and polyvinyl chloride. Nevertheless, a definite amount of permeation remains even in the best plastic due to the molecular arrangement thereof.
Composite blow molded containers have been prepared as described in my prior U.S. Pat. Nos. 3,719,735 and 3,717,544. According to said patents, previously formed sleeve-like liners are applied to a blow core of an injection blow molding apparatus, plastic is injected around said liners while upon the cores, and the resultant composite parison consisting of the liner and the injected plastic is expanded together into conformance with a blow mold. While these composite containers represent a considerable improvement due particularly to their ability to combine properties of different plastics, one of which may be a barrier plastic, a definite amount of permeation still remains even in these improved materials.
As a result, a new factor must be introduced whenever it is desired to package perishables in plastic or other partially permeable materials, namely shelf-life. While a metal can or glass jar will keep its contents unchanged for a practically indefinite period, a time limit, mostly in terms of weeks, must be prescribed for the plastics, modified paper, etc.
Accordingly, it is a principal object of the present invention to provide a method for the preparation of multilayered, hollow plastic containers having improved resistance to gas permeation, especially air permeation, and also to provide an improved container.
It is a further object of the present invention to provide a method as aforesaid which is inexpensive and convenient and which utilizes a partially permeable barrier material in an arrangement which signficantly increases the resistance of the container to gas permeation.
Further objects and advantages of the present invention will appear hereinafter.